1. Field of the Invention
The present invention is directed to electrically conductive and electromagnetic radiation absorptive coating compositions and the like.
2. Brief Description of the Prior Art
A variety of coating compositions are known which have electrically conductive or electromagnetic radiation absorptive properties or the like. The solvent for many of the coating compositions has been primarily a volatile organic compound (VOC). A VOC-based binder system has several drawbacks. It may be toxic, flammable, and possibly explosive. The VOC raw material is costly to purchase and the waste is expensive to discard. Generally, VOC solvent emitted from coating operations is an environmental air pollutant. Expensive equipment and procedures are required to capture and contain VOC solvent emissions in order to reduce air pollution and enable proper waste disposal.
Coating compositions are also known which use electrically conductive or electromagnetic radiation absorptive microspheres. However, these coating compositions have been limited by the binder systems employed.
Finally, coating compositions are known which use a plurality of electrically conductive particles. However, these coating compositions have also been limited by the binder systems employed.
Accordingly, it is an object of the present invention to provide an aqueous based coating composition having electrically conductive or electromagnetic radiation absorptive properties or the like.
It is a further object of the present invention to provide a coating composition which is electrically conductive or electromagnetic absorptive or the like having an improved binder system.
These and other objects of the invention will become more apparent upon reading the following description of the invention.
The present invention is directed to an electrically conductive or electromagnetic radiation absorptive coating composition or the like having a water soluble emulsion polymer binder. The binder is a blend of a first emulsion containing a conjugated diene monomer or comonomer, and a second emulsion containing an acrylic polymer. The first emulsion preferably includes an ethylenically unsaturated comonomer which is typically an unsaturated nitrile such as acrylonitrile, a monovinyl aromatic hydrocarbon such as styrene, or vinylpyridine. The first emulsion is preferably a substantially saturated carboxylated or non-carboxylated butadiene-acrylonitrile latex. The carboxylated butadiene-acrylonitrile latex preferably contains unreacted salts.
The coating composition also contains an effective amount of electrically conductive particles dispersed in the binder. The particles include a combination of graphite particles, and metal containing particles. The graphite particles are preferably natural flake graphite. The metal containing particles are preferably silver or nickel containing particles. The silver or nickel containing particles are more preferably silver or nickel coated ceramic microspheres which may have electromagnetic radiation absorptive properties.
The coating composition also contains water. The water is present in a solvent effective amount.
The present invention further relates to a coated substrate. The substrate is typically paper, cloth, plastics such as polycarbonate, acrylic, nylon and polyester, rubber, steel or fiberglass. The substrate may be a plastic component of an electronic device. The substrate may also be a pipe, a rubber mat, or the like. In the case where the metal containing particles are electromagnetic radiation absorptive microspheres, the substrate is typically a vehicle such as an aircraft.